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azoblue passes along a story in the Washington Post, which begins:
"NASA's Mars Meteorite Research Team reopened a 14-year-old controversy on extraterrestrial life last week, reaffirming and offering support for its widely challenged assertion that a 4-billion-year-old meteorite that landed thousands of years ago on Antarctica shows evidence of microscopic life on Mars. In addition to presenting research that they said disproved some of their critics, the scientists reported that additional Martian meteorites appear to house distinct and identifiable microbial fossils that point even more strongly to the existence of life. 'We feel more confident than ever that Mars probably once was, and maybe still is, home to life,' team leader David McKay said at a NASA-sponsored conference on astrobiology."

If any fossilized life they find their has the same four nucleotides in its dna sequence (assuming anything like DNA can be recovered), then it is far more likely that the fossils are from Earth and have contaminated the sample. If, however, some sort of dna material can be obtained and there are different base nucleotides, then we have a winner.

Actually I'd be a little surprised if the nucleotides were different, current studies seem to suggest that the nucleotides had selective pressure. Here's a video that summarizes some current work on abiogenesis by Dr. Jack Szostak. http://www.youtube.com/watch?v=U6QYDdgP9eg [youtube.com]

Hard to believe there's not someplace on Earth where the same nucleotide variations would have been advantageous.

Yeah, and it's quite plausible that at the dawn of primitive life, there were several variations, but only this one survived. Life probably got nearly wiped out many times back then, considering all the meteorities, volcanic activity, probably not-yet-quite-stable sun... So our current encoding is probably the one that was best in an environment that didn't get sterilized when everything else got sterilized at some point.

But once the encoding sets in, once there's actual xNA with information, changing encod

How could a fossil that is few billion years old be of Earth origin, if the meteorite is here for only a very short time?

Anyway, if we would rely mostly on comparing things like nucleotides (not that they actually can)...well, that bit of information doesn't have to provide us with definite answer at all. With life that is so old, we aren't certain at all that Earth life relied on "the same four nucleotides" back then. Heck, it might have been that, while Earth life was different, the one on Mars was by a r

Beyond that, if they are the same, then it may not be coincidence at all. One planet's life may have been seeded by the other, or both come from another common origin, whether deliberately by intelligent beings, or indeliberately by chance.

The problem is that there are all kinds of inorganic deposits that look a lot like fossil bacteria. Differentiating between them is very, very difficult. The standards are pretty high for declaring things to be ancient microbial fossils from Earth, and even then there are mistakes and debates. The standard for something from Mars has got to be even higher, and when all you have is an oblong shape that is very, very small, well, it's not very strong evidence.

I wasn't even touching on this subject. Sure, there is a considerable debate if those are really fossil bacteria.

But determining how old those structures are is considerably easier. Likewise - determining from where the meteorite, in which they are embedded, came from and how long it has been on Earth.There is very little uncertainty that those structures are Martian, which was what GP poster doubts.

then it is far more likely that the fossils are from Earth and have contaminated the sample

First, meteors are easily identifiable as coming from outer space due to the structure of the rock i.e. melted exterior but not interior, material composition matching Mars, and carbon dating. Second, this particular meteor [wikipedia.org] was found embedded in ice in Antarctica as many meteors are found. How did it get there? (Antarctica is a great place find intact meteors because the ice buffers the landing and then protects the

They can't carbon date stuff from Mars, because carbon dating has to be done on things that formerly were alive. Heck, it depends on the properties of our atmosphere -- the fact that the carbon there has a certain isotope makeup, and that we know how this makeup has been changing over history. The carbon dating calibration curves describe history of Earth's atmosphere, not some other random atmosphere.

They can date stuff from Mars using other isotopes that have longer half-lives, and are somehow related to

They can't carbon date stuff from Mars, because carbon dating has to be done on things that formerly were alive.

That's not incorrect, but not because things the you are going to date with carbon dating need to have been alive. They need to have been in equilibrium with the atmospheric carbon pool before they went out of equilibrium - which a living thing does by dieing, but a non-living thing could do, for example, by being buried in sediment.The ultimate constraint on carbon dating (and any dating system)

The featured article talks about magnetite possibly formed by microbes. There is no mention of nucleotides. How can organic molecules from microbes survive fossilization for billions of years, form part of a meteorite, survive its journey through our atmosphere and yet be analyzed?

After all, it would be an extremely rare chance to find surviving DNA from even dinosaur fossils here on earth. The scientific method followed for studying genetic evolution happens mostly by triangulation of molecular informatio

We cannot discount that this is the only feasible working chemistry for life, therefore possible life from mars could only have this configuration. Has anyone shown there are possible different base nucleotides for example? Are there are organisms on earth with any differences at such fundamental levels? I haven't heard of any.

There's a study recently released from MIT that outlines an early life stage DNA in molecule sized fossils found in ancient rocks. Perhaps the MIT folks can look at the Mars asteroids for evidence of molecules that imply life encoding DNA. http://web.mit.edu/newsoffice/2010/gene-fossils-0506.html [mit.edu]

DNA breaks down pretty quickly, in geologic time. The will not find intact strings of DNA in ALH84001, period, and actually looking for living organisms on Mars is going to be very difficult.

Also, if we some day find microorganisms on Mars that share the genetic code of Earth's life, that doesn't prove it's not native Mars live; panspermia and selection both could reasonably explain it. Finding a different code, however, would be excellent evidence for unique origin or long, indpendent evolutionary histo

There's no smoking gun, that is, some direct evidence of these organisms. And frankly, I don't find the current claim of relatively pure magnetite to be compelling. This is part of why I've bet against the discovery of alien life by 2050 [ideosphere.com] since 1996.

While it may be cool to find life on Mars, it would present some additional problems for future colonization (or even just future missions, robotic or otherwise). If we do find life, do we quarantine Mars so that we don't contaminate the native life there? Do we bar ourselves from any terraforming efforts whatsoever so that we don't disrupt possible existing life? You all must realize that that would be the position of at least some people; what percentage of the public that might be, and the influence they would have is another question.

Generally, I think it would be much simpler if we never found life on Mars, and could in fact say with a fair amount of certainty that it is completely dead. That would remove a (possibly significant) reason to oppose human colonization and terraforming.

If we do find life, do we quarantine Mars so that we don't contaminate the native life there? Do we bar ourselves from any terraforming efforts whatsoever so that we don't disrupt possible existing life?

While it may be cool to find life on Mars, it would present some additional problems for future colonization (or even just future missions, robotic or otherwise). If we do find life, do we quarantine Mars so that we don't contaminate the native life there? Do we bar ourselves from any terraforming efforts whatsoever so that we don't disrupt possible existing life? You all must realize that that would be the position of at least some people; what percentage of the public that might be, and the influence they would have is another question.

I think here that we'll just have to take it as the universe gives it to us. If there is life on Mars, we will probably establish some sort of barrier so that Earth life doesn't necessarily contaminate Mars life and vice versa. Even if Mars colonization turns out to be obstructed by regulation or other means to prevent contamination, the obstacles will be reasonable or someone will find a way to get around the regulations in question (say by totally ignoring them and deliberately contaminating Mars and/or E

Besides War of the Worlds scenarios, life is robust enough to beat foreigns. See smallpox and the new world, though it wasn't pretty, life still lived. Its just Darwinian is all. Get used to alien life and death, its a coming, probably jump out of your chest style.

How many trips would that take?What kind of volume are we talking about here?What kind of time frame are we looking at?

We need some calculations so that we can make ourTitan gas hauler large enough to get the job donein a reasonable amount of time. Is there enoughmetal in our solar system to make a space craft large enoughto haul that much gas in a reasonable amount of time?

I think human made space stations are probably a better bet.Terraforming is a fantasy that doesn't add up.

I used to be naive and idealistic like you, then I learned about panspermia. It is fairly certain by now that all planets are being bombarded by asteroids filled with random organisms. Earth and Mars have almost certainly been recipients of foreign material. Any bacteria, etc. that we might transfer to Mars should cause us no worries. Organisms from Earth should be just as valid as random organisms from panspermia. In fact the very organisms that we might take there could have been derived from our own expo

I used to be naive and idealistic like you, then I learned about panspermia. It is fairly certain by now that all planets are being bombarded by asteroids filled with random organisms. Earth and Mars have almost certainly been recipients of foreign material. Any bacteria, etc. that we might transfer to Mars should cause us no worries. Organisms from Earth should be just as valid as random organisms from panspermia. In fact the very organisms that we might take there could have been derived from our own exposure to panspermia.

Speaking of smoking guns, where's the asteroid or comet with life on it? For panspermia to be valid, there need to be evidence of life in space. We haven't observed that yet (aside from some bacteria spores in the upper atmosphere, which might become cast off from Earth). Further, just because Mars and Earth might have organisms from the same common source, doesn't mean that they'll live peacefully together. On Earth, we have plenty of examples of invader species that upend an ecosystem in which they have n

Panspermia doesn't really answer where life comes from. It just sort of shifts the question off of Earth. When someone asks, "How did life come about?", the least informative answer you can give them is that it was seeded here by an asteroid or meteor. The real question is how did it arise on the object that the seeding object came from. Panspermia's just a cop-out.

Panspermia doesn't really answer where life comes from. It just sort of shifts the question off of Earth.

It's true, it doesn't answer where life comes from, but it's more than turtles all the way down. Shifting the question off Earth changes the question, because off Earth the conditions are different! Panspermia removes all objections related to the specific conditions of primeval Earth. If you postulate that life has appeared on Earth, your theory has to explain it given a lot of constraints: a certain c

Most microorganisms from earth cannot survive outdoors on Mars, so hopefully the (hypothetical) Martian native life will not be contaminated.
But frankly I don't think that any country on earth will delay colonization of Mars to save its native life.

[...] If we do find life, do we quarantine Mars so that we don't contaminate the native life there?[...]

Depends on the means used to find that life form and the motivation to go to Mars. If (say) China decides to colonise Mars as a means to ensure that human life goes on even if the Earth becomes uninhabitable, I do not think that other countries would shoot down their colony ships on the basis of preserving a pristine state of the Martian nature.
I'm sure there are international treaties about space exploration and ethics in space, but if there's an emergency or a huge amount of money waiting for a very limi

"do we quarantine Mars so that we don't contaminate the native life there?"

Of course not. Are you nucking PHUTTS? If there's life on Mars, or anywhere else, we'll CULTIVATE it and EAT IT!! Do you know what nutrients those Martian slugs need? Mine aren't doing so well, right now. Maybe a little acetic acid?

...and will get along just fine even if we move into the neighborhood.

People really need to *Get Over* the whole Star Trek thing and worrying about everybacillus/eucaryot and rock as if it were some precious message from an all knowing spaghetti-monster."Oh my god, I moved a rock!!!!!"

Mars is the house next door. If it's on Mars, it's probably here already too, and vice versa.

The main proponents of staying in Earth are those who would lose a great deal of socialcontrol over the masses. Protecting microbes

As for terraforming Mars, Venus is a better bet. Gravity is similar, it's inside thetemperate zone and it's atmosphere has the makings of water.

Mars has a CO2 atmosphere for a reason. It's gravity is too low to keep oxygenfrom blowing away in the solar wind.

Actually Venus has lost most of its hydrogen so doesn't have much in the way of water makings.And Mars has a CO2 atmosphere for the same reason as Venus. Oxygen is reactive and combines with hydrogen or carbon (usually) rather then existing as an elementary element.The only reason that the Earth has free oxygen is due to life.

It is my understanding that bacteria could survive a trip through space from Earth to Mars (or vice versa). I wonder if a chunk of earth made it to Mars and seeded Mars with bacterial life. That could mean that the bacterial life on Mars could have the same characteristics as bacterial life on Earth because they originated from Earth. It makes the contamination issue a little more complex.

...and we still find life on Mars. It would be pretty exciting to find out that life started on Mars and came here, but how much more exciting would it be to find out that two different forms of life started on two different planets in one solar system? With odds like that, I'd be willing to bet that the universe is just crawling with life.

If it's true, it's actually not a huge deal. I could mean that life spontaneously started on both Earth and Mars (Panspermia). But it's probably more likely (Occam's razor and such) that life started on either Earth or Mars and was transported via meteor to the other planet.
I would be very cool if life on Earth actually started on Mars, but it's not clear to me how we could prove which came first.
-S

I feel that this notion ingrained in to our environmental education that anything and everything human beings do is bad and/or unnatural is just wrong.
The universe is a vast place. And in the big picture, we are all part of it. Nothing we could possibly do is out of the bounds of nature on a universal scale. We have as much right to explore, seed, and shape the cosmos as any other creature in the universe. If we disturb the habitat of any other planet, so be it. It's the laws of the universe at work.

To paraphrase Carl Sagan...
The cosmos is within all of us. We are made of star stuff.

I feel that this notion ingrained in our environmental education that anything and everything human beings do is bad and/or unnatural is just wrong.
The universe is a vast place. And in the big picture, we are all part of it. Nothing we could possibly do is out of the bounds of nature on a universal scale. We have as much right to explore, seed, and shape the cosmos as any other creature in the universe. If we disturb the habitat of any other planet, so be it. It's the laws of the universe at work.

..and I reject the notion that my urinating on your doorstep is in any way unnatural.

Its called having respect for something that isn't yours. Get some, and stop whining that other people might actually hold you accountable for the consequences of your actions, since you are apparently too selfish or short-sighted to consider them on your own.

Easy to say when you're not on the receiving end. What if some alien civilization decided Earth looked like a good place to hang out when we were still crawling out of the ocean?

Sounds like you're saying it's alright to take what you want if you have the power and no one can stop you. Nazis and Poland, Europeans and the New World, Sky People and Pandora... just take what you want. I think we should tread carefully. We may destroy something irreplaceable before we recognize its value.

s/exists/ever existed/.Unknowable given our current state of science, but some theories would place it quite high.

x (probability a comet hits Mars and expels some rocks with bacteria inside)

Given that life existed, this is almost certain to have happened, probably many times. We know that rocks have been expelled via such a mechanism. We know that in a biosphere like Earth's, it is almost impossible to find surface-level rocks that don't have any signs of life. We wo